Family Name ……………………………….. Given Name ………………………………… Student No. …………………………………. Signature ……………………………………
THE UNIVERSITY OF NEW SOUTH WALES School of Electrical Engineering & Telecommunications MID-SESSION EXAMINATION
S1 2016
ELEC1111
Electrical Circuits
TIME ALLOWED:
TOTAL MARKS:
TOTAL NUMBER OF QUESTIONS:
55 minutes 40
5
THIS EXAM CONTRIBUTES 20%TO THE TOTAL COURSE ASSESSMENT
Reading Time: 5 minutes.
This paper contains 3 pages.
Candidates must ATTEMPT ALL questions.
Answer all questions in the answer booklet provided.
Marks for each question are indicated beside the question.
This paper MAY be retained by the candidate.
Print your name, student ID and question number on the front page of each answer book. Authorised examination materials:
Candidates should use their own UNSW-approved electronic calculators.
This is a closed book examination.
Assumptions made in answering the questions should be stated explicitly.
All answers must be written in ink. Except where they are expressly required, pencils may only be used for drawing, sketching or graphical work.
QUESTION 1 [4 marks]
For the circuit in Figure 1 below, calculate the equivalent resistance 𝑅𝑒𝑞 of the network as seen from the terminals shown.
3Ω
4Ω 6Ω
4Ω
Figure 1
5Ω
Req
QUESTION 2 [8 marks]
6Ω
For the circuit below in Figure 2, apply nodal analysis, and write down the node voltage equations using the labels shown in Fig. 2. Note: You should NOT solve them.
v14Ωv2 v33Ωv4
+v-
1A 2Ω 1Ω 5Ω +- 2v
Figure 2
QUESTION 3 [8 marks]
For the circuit shown below in Figure 3, use mesh analysis to write down mesh equations and solve for the mesh currents labelled 𝑖1, 𝑖2, and 𝑖3.
4Ω
3Ω i3 2Ω
2V i1 1A i2 Figure 3
1V
Page 2
QUESTION 4 [12 marks]
(a) (6 marks) For the circuit below in Figure 4, showing sketches in your working, use the superposition principle to determine the current i that flows in the 20 resistor.
(b) (6 marks) Using source transformation, find the Norton equivalent of the circuit to the left of the terminal pair A-B in Figure 4.
20
QUESTION 5 [8 marks]
6A
30
30
Figure 4
A 10V
20 i
B
For the circuit below in Figure 5, the switch has been in the same position for a long time before changing position as shown at time t = 0.
(a) (4 marks) Calculate the capacitor voltage 𝑣𝐶(𝑡)
(i) immediately after the switch closes, i.e. 𝑣𝐶(0+), and (ii) as 𝑡 → , i.e. lim𝑡→∞ 𝑣𝐶(𝑡) .
(b) (4 marks) Give an expression for the capacitor voltage 𝑣𝐶(𝑡) (i.e. as a function of time) for t > 0. Explain how you arrived at this expression.
3Ω
+
3Ω 0.1F -vC(t) 3Ω
Figure 5
END OF PAPER
6A
t=0
5Ω
Page 3